Aiming a rifle or gun requires the consideration of several environmental and other types of factors. When a bullet travels from a rifle to an intended target, several forces affect the flight of the bullet. Gravity causes the bullet to drop in elevation as the bullet travels from the firearm to the target. If a hunter is close to his/her target, as shown in FIG. 1A, the bullet drops very little, represented by the adjusted trajectory 100. However, improvements in firearms and ammunition have allowed hunters to target game from long distances. At these greater distances, gravity causes a bullet to drop in elevation more significantly, as represented by the adjusted trajectory 102 in FIG. 1B. Other factors also affect the flight of the bullet. For instance, wind causes the bullet to move horizontally along the bullet's path of flight. The compensation in a riflescope for the effect wind has on a bullet's flight is often referred to as windage. Humidity, elevation, temperature, and other environmental factors may also affect the flight of the bullet.
Different bullets fired from a gun are affected to a greater or lesser degree by environmental factors. Some bullets have a greater mass, e.g. a .223 caliber bullet has a mass of 55 grains while a .338 Mag bullet has a mass of 225 grains. The more massive bullets are affected less by wind and some other environmental forces. In addition, some bullets travel at higher speeds than other bullets, which also affect the flight of the bullet. All of these factors create a unique bullet trajectory for every shot taken from a rifle.
A hunter, sniper, or other person using a rifle or other firearm, commonly referred to as riflemen, use sighting systems, such as riflescopes, to visually acquire a target and improve their aiming accuracy. Generally, riflescopes provide a magnified field of view 200 of the target 208, as shown in FIG. 2A. By placing an intended target 208 within the field of view 200 defined by a field stop 202 and aiming the rifle with the crosshairs 204 and 206, the riflescope improves the aiming accuracy for a rifleman for shots taken over long distances. Many riflescopes provide a reticle, which is an aiming device superimposed on the field of view 200 and consists of a vertical crosshair 204 and a horizontal crosshair 206. A hunter can use the intersection 210 of the vertical 204 and horizontal 206 crosshairs to aim the rifle. By placing the intersection 210 over the target 208, at longer distances, the hunter can deliver the bullet to the aiming point represented by the intersection 210.
Riflemen must consider and adjust to the different environmental factors and bullet characteristics explained above to ensure the bullet effectively hits the target. To adjust for the bullet trajectory, a rifleman must raise the rifle and effectively aim over the target such that, as the bullet drops along the bullet's flight path, the bullet will still strike the target. For example, the rifleman must place the intersection 210 of the crosshairs above the target 208, as shown in FIG. 2B. This adjustment in aiming is called hold over. Some riflescopes help riflemen with correctly aiming for hold over.
Some reticles include a series of hatches or marks along the vertical and/or horizontal cross-hairs. The hatches can be used to compensate for hold over or windage. Unfortunately, the hatches are generally not labeled and the rifleman must understand which hatch to use for his/her needed bullet type and range to the target. Thus, the riflemen, even with a scope, must determine how to aim the gun using the hatches, and this determination is often inaccurate, which leads to the rifleman missing the intended target.